Process for refining alloys of lead and tin



Patented Nov. 24, 1936 PROCESS FOR REFINING ALLOYS OF LEAD AND TIN Jesse 0. Betterton and Yurii E. Lebedefl, Me-

tuchen, N. J., assignors to American smelting and Refining Company, New York, N. Y., a poration of New Jersey No Drawing. Application October 11, 1935, Serial No. 44,539

7 Claims.

This invention relates to the treatment of impure lead-tin alloys and provides a process for refining such alloys with respect to antimony as a. contaminant.

While the refining of so-called white metal alloys has received considerable attention on the part of metallurgists by reason of the relatively high commercial value of their solder contents, nevertheless processes designed to recover the solder in a pure state have met with considerable difficulty from the standpoint of economic operation by reason of the sacrifice of prohibitive quantities of the lead-tin alloy itself in order to reduce the impurities, particularly antimony, to within the limits of market tolerance.

By treating an impure lead-t n alloy with zinc, it is possible to remove'as a dross substantially all the arsenic and copper originally contained in the alloy and to reduce the antimony content of same from, say, 12% to approximately 1%-l.5%, the metal so treated remaining saturated with zinc. However, a reduction of the antimony content to only such a point is insufficient for many purposes.

The present invention provides a process for treating lead-tin alloys by which the antimony content is readily lowered to materially less than 1% in a very efiicient manner.

In accordance with the invention, a bath of the impure lead-tin alloy contaminated with antimony, for example, solder metal which has been refined with zinc as indicated above, is treated with an alloy of calcium and zinc. In adding the calcium-zinc alloy to the bath, the latter is brought to a temperature permitting the ready introduction and solution of the alloy, a temperature in the neighborhood of approximately 950 F. giving good results when using an alloy comprising 43.5% calcium and 56.5% zinc which is well within the range of composition having the lowest melting point of the calcium-zinc series of alloys.

Upon thoroughly stirring the calcium-zinc alloy into the bath, the antimony is concentrated in the form of drosses or crusts and this action is facilitated by cooling the bath. By liquating the drosses and crusts much of the entrained metal of the bath proper can be removed and returned to the bath.

A feature of the invention resides in the fact that most of the antimony capable of removal by the instant process is effected without lowering the bath to its freezing temperature. As a result the antimony can be removed at a somewhat higher temperature and thereafter the bath lowered to freezing to recover practically all the remaining calcium and'zinc in excess of saturation as a final crust which is admirably suited for treating additional quantities of impure white metal alloys.

The following example is illustrative of the process: impure solder metal which had been given a preliminary refining with zinc as above described was melted in an ordinary, open, castiron refining kettle and skimmed. To the initial metal which had been heated to approximately 950 F., there was added a calcium-zinc alloy (Ca, 43.85%-Zn, 56.4%) in amount just slightly more than 2% of the weight of the bath which was the quantity calculated to effect a clean-up of the antimony. Complete solution of the alloy was effected in about 15 minutes by stirring with a mechanical mixer, the bath being maintained within a range of about 940 F. to about 980 F. The bath was then cooled to about 800 F. and the dross skimmed as formed. The bath was then cooled to freezing and the crusts separated from the final metal. The analyses of the initial bath, dross, crusts and final bath are given in percentages in the following table:

5 Dross Crusts Final bath Antimony e QUINN Calcium The composition of the calcium-zinc alloy may vary between relatively wide limits and the quantity used will, of course, largely depend upon the amount of available calcium and zinc in the particular composition employed. A suitable composition of the alloy, for convenience, lies in the approximate neighborhood of equal parts of calcium and zinc.

The zinc remaining in the final metal is readily removed by any of the well-known processes, such as oxidation or chloridization.

It will readily be appreciated from the results given that in addition to greatly diminishing the antimony content, the process is advantageous in that the final crusts are admirably suited for re- 50 use in the process for treating further quantities of impure lead-tin alloys, thus making for marked economy of operation which is an important consideration in the treatment of white metal alloys as heretofore pointed out.

What is claimed is: l

l. The process for refining impure solder metal with respect to antimony as a contaminant which comprises incorporating a calcium-zinc alloy in a bath of such metal, cooling the bath and separating the resulting drosses therefrom, further cooling the bath to freezing, effecting a separation between the refined metal and frozen crusts and returning said crusts to the process in treating a subsequent bath of impure solder metal.

2. The process for treating a lead-tin alloy con-4, taining a relatively small but objectionable quantity t antimony which comprises establishing a molten bath of the alloy, incorporating a calciumzinc alloy therein, cooling said bath and eflecting a separation between the resulting antimonial dross and the alloy.

3. The process for refining impure solder metal which comprises initially refining the impure metal with zinc, and further refining the zinc-refined metal by reacting upon the same with additional quantities of zinc in the presence of calcium thereby throwing out from solution in the solder metal substantially all of residual impurities including antimony.

4. The process for refining solder metal with respect to antimony which comprises incorporating a calcium-zinc alloy in a bath of the metal at a temperature of approximately 950 F. and cooling the resulting bath thereby separating out antimony in the form of drosses and/or crusts.

5. The process for treating alloys comprising principally antimony, lead and tin which consists in first refining such alloys with zinc and then subjecting the partially refined alloys to a second refining operation employing a calcium zinc a1- loy reagent thereby yielding substantially pure solder metal.

6. The process for treating antimony-bearing solder metal which consists in initially refining a molten bath of such metal with zinc and further refining the resulting metal with calcium in the presence of zinc thereby eflect'ing a substantially complete elimination of the antimony from the solder metal.

7. In the process for refining a bath of antimony-bearing solder metal with calcium, that improvement which comprises reacting the calcium with the bath in the presence of zinc.

JESSE O. BETTERTON. YURII E. LEBEDEFF. 

